Intermediate product



Unite States METHOD OF MAKING CYANURIC ACID AND INTERMEDIATE PRODUCT Ludwig J. Christmann, Bronxville, N.Y., assignor to Carbogen Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Dec. 17, 1957, Ser. No. 703,263

8 Claims. (Cl. 260-248) atetitO It is well known that cyanuric acid is formed when urea is heated substantially above its melting point. Howfever, when this operation is carried out on a large scale,

wields are low. On a commercial scale it is difiicult to fiecover the reaction products because of the tendency of the material to stick to the walls of the vessel. Moreover, the grade of cyanuric acid so produced is quite low and for many purposes a high grade material is required. Purifying cyanuric acid is difficult because of its poor solubility characteristics and the tendency of some of the impurities to crystallize with the cyanuric acid.

Another method of the prior art is to heat urea with anhydrous zinc chloride to about 220 C. After cooling the product is treated with dilute hydrochloric acid and the crystals which separate are recrystallized from hot water. Yields are low and on a commercial scale, for economy, it would be necessary to recover the 'zinc chloride for re-use. Such an operation is costly. The use of hydrochloric acid adds to the cost and introduces additional corrosion problems.

Various media have been suggested as means for heating urea to reaction without resulting adhesion to reaction vessel walls and to assist in the conduction of heat into the molten urea. Paraflin, phenols, cresols and esters such as adipic acid esters, etc., have been suggested. While these materials may help in the mechanical aspects of the process, they do not give a high quality product. In fact, some materials such as phenols discolor the product and impart a disagreeable odor. Even when such a phenol is removed from the product there remain potentially colored compounds which appear, for example when the cyanuric acid is chlorinated to produce chlorocyanuric acid. Chlorocyanuric acid is a commercial product used as a bleaching agent.

It has also been proposed to heat urea with amyl alcohol under a reflux at atmospheric pressure in order to produce cyanuric acid. Such a procedure was inetficient in that the time of reaction was too low due at least in part to the lack of solubility of urea in the amyl alcohol. The yields were quite low, the product was impure and it was difiicult to recover the cyanuric acid from the reaction mass. Therefore, it has not gone into commercial use.

The present invention is intended to overcome the difficulties and disadvantages inherent in prior processes of the type described, it being among the objects of the present invention to provide a simple and direct process for converting urea to cyanuric acid.

It is also among the objects of the present invention to provide a process of making cyanuric acid which will result in a product of high purity and a high yield approaching the theoretical yield.

It is further among the objects of the present invention 5 hours.

to provide a process for producing an intermediate prodnet of urea which acts as a solvent for urea and promotes a smooth reaction to form cyanuric acid.

The invention is based on the discovery that there are certain organic compounds which have a high solubility for urea at elevated temperatures and that when urea'is dissolved in these compounds at the elevated temperatures and heating continued, cyanuric acid is formed. The overall equation for the reaction is as follows:

3NH2C 0NH (CNOH) a-HiNHa III'GB cyanuric ammonia acid An important feature of the invention is the re-use of the medium, which, as is described below, appears to be not the original compound but a reaction product of this compound and urea.

In practicing the invention, a mixture is made of an ether-alcohol and urea, the ether-alcohol having the following general formula wherein m=l-6, n=1-17 and m+n=2 or more. The ether-alcohols have boiling points up to about 290 C. and the reaction is caused to take place at temperatures between and 350 C. Preferably the ether alcohols have boiling points over about C. at atmospheric pressure, but lower boiling ether-alcohols such as those boiling at about 125 C. may be used under superatmospheric pressures. A considerable number of etheralcohols may be used such'as the methyl, ethyl, propyl and 'hexyl ethers of ethylene glycol and diethylene glycol. Also applicable in the present invention are polyethylene glycols having a molecular weight up to about 400.

The method involved may in theory be divided into three steps or stages. In the first stage, the reaction is conducted at the elevated temperature, preferably with stirring to cause evolution of ammonia and at the stage where a homogeneous solution is formed, an intermediate product which is a carbamate is formed. In the next stage, the heating is continued in the presence of additional urea dissolved in the carbamate until evolution of ammonia has ceased, showing the completion of the reaction. Preferably this reaction is conducted at temperatures of about to 250 C. The cyanuric acid formed precipitates from the solution. The third stage of the operation consists in the separation of the cyanuric acid from the mother liquor, usually by the use of a primary alcohol having 1 to 3 carbon atoms. The recovered mother liquor is then used in additional cycles by the introduction of urea and conducting the reaction again to produce cyanuric acid. This cycle may be repeated a considerable number of times.

The following are specific examples of some of the procedures in practicing the invention.

Example 1 120 cc. of diethylene glycol monomethyl ether were heated with 120 g. of urea under reflux for two hours, during which time ammonia was evolved and cyanuric acid separated. The slurry was cooled and 60 cc. of methanol were added. The slurry was filtered and washed with further methanol. The dry cyanuric acid cake weighed 26 g. The methanol was removed from the combined mother liquor and the wash liquors by distillation, 120 g. more of urea was added to the remaining residue, and the mixture heated under reflux for two Cyanuric acid again precipitated after cooling, 60 cc. of methanol was added and the slurry filtered. The cyanuric acid cake was Washed with methanol and dried. Dry weight was 79 g. The mother liquor and the wash liquors from this stage were distilled to remove the methanol, 120 g. of urea was added to the remain- Patented Mar. 14, 19 61 Example 2 It is preferable to conduct the reaction at temperatures of 190 to 250 C. At these temperatures a higher grade product results. The impurities that form at lower temperatures are present in much smaller amounts at higher temperatures. It is probable that at the lower temperatures biuret is formed, and that biuret reacts with some of the precursors of cyanuric acid, perhaps cyanic acid, to form undesirable impurities.

A mixture of 240 grams of diethylene glycol monomethyl ether (2 mols) and 240 grams of urea (4 mols) was heated under reflux. At 114 C. a clear, homogeneous solution was obtained. This was heated to 210 C. in 135 minutes. Ammonia was evolved. A very small amount of precipitate was filtered off and dis carded. This intermediate mixture was divided into two equal parts of 175 cc. each.

To one 175 cc. portion of above mixture 120 grams of urea were added. The temperature was raised from 185 C. to 222 C. in 45 minutes during which time cyanuric acid precipitated. The mixture was cooled, 100 cc. of methanol were added. The cyanuric acid was filtered otf, washed with 100 cc. of methanol and dried. There were obtained 81 grams of cyanuric acid 85.9% pure.

To the other 175 cc. portion of the intermediate mixture, 120 grams of urea were added and the mixture refluxed. In 143 minutes the temperature was raised from 140 C. to 200 C. Cyanuric acid precipitated. To the cooled mixture 100 cc. of methanol were added. The solid was filtered off, washed with 100 cc. methanol and dried. There were obtained 60 grams of cyanuric acid 58.6% pure.

A comparison of the results indicates the importance of the higher temperatures for the reaction of urea to cyanuric acid.

Example 3 Impurities in some lots of commercial methyl ether of diethylene glycol cause colored bodies to form and may otherwise interfere with the smooth course of reaction. Therefore, this medium is purified by distillation to provide a material boiling within a narrow range, say 2 C. Where practicable it is also preferred to purify the other solution media used in the other examples below.

A mixture of 180 grams of the distilled diethylene glycol mono-methyl ether (1.5 mols.) and 190 grams of urea (3.16 mols) was heated under reflux. At 120 C. a homogeneous solution was obtained. The temperature was raised from 120 C. to 231 C. in 85 minutes. During the interval solid cyanuric acid precipitated. The mixture was cooled and 100 cc. of methanol were added. The solid was filtered off, washed with 100 cc. of methanol and dried. There were obtained 46 grams of cyanuric acid, 95.5% pure.

The methanol was distilled from the above mother liquor and 190 grams of urea were added. The mixture was heated under reflux, the temperature rising from l70233 C. in 100 minutes. Solids precipitated. The mixture was cooled and 100 cc. of methanol added, the solids were filtered oif, washed with 100 cc. of methanol and dried. There were obtained 117 grams of cyanuric acid analyzing 96.5%.

The procedures of the above paragraph were repeated twice. There were obtained 148 grams of cyanuric acid in the first case and 149 grams in the second, both crops analyzing 97%. The last mother liquor was practically water-white and could be used again.

Example 4 This work has led to the theory that what first occurs is a reaction of urea with the ether-alcohol evolving ammonia and resulting in the formation of a new compound, probably a carbamate of the ether-alcohol. This carbamate then serves as the solvent in which reaction of additional urea takes place. This reaction also evolves ammonia. In the present process, the cyanuric acid is separated from the medium, the carbamate of the alcohol-ether is recovered and used over again. This makes for economy. Time cycles are reduced because it is unnecessary to make the carbamate for subsequent runs. The carbamate forming reaction is usually slower than the cyanuric acid forming reaction.

In this procedure the intermediate is first formed and then used as the heating medium for making cyanuric acid.

A mixture of grams of diethylene glycol monomethyl ether (1 mol.) and 60 grams of urea (1 mol.) was heated under reflux. A homogeneous solution was obtained at 108 C. The mixture was heated from 108 C. to 231 C. in 56 minutes. Ammonia was evolved. No appreciable solids separated. A slightly translucent solution was obtained on cooling. By this procedure the medium for the cyanuric acid reaction was formed. Sixty grams of urea (1 mol.) were then added to this medium and the mixture heated under reflux from C. to 233 C. in 89 minutes. During this interval cyanuric acid precipitated. On cooling 100 cc. of methanol were added, the solids filtered off, washed with 100 cc. of methanol and dried. There were obtained 29 grams of cyanuric acid analyzing 99%.

After distilling off the methanol from the mother liquor 60 grams of urea were added and the mixture heated under reflux. The temperature was raised from 140 C. to 236 C. in 64 minutes and precipitation occurred. On cooling 100 cc. of methanol were added, the solids filtered off, washed with 100 cc. of methanol and dried. The yield was 44 grams of 99.7% cyanuric acid.

The methanol was distilled from this mother liquor, 120 grams of urea (2 mols) were added and the mixture was heated under reflux. The temperature was raised from C. to 231 C. in 56 minutes. Precipitation occurred. To the cooled mixture 100 cc. of methanol were added, the precipitate was filtered, washed with 100 cc. of methanol and dried. The cyanuric acid weighed 83 grams and analyzed 98.5%.

The procedure of the last paragraph was repeated except that grams of urea were used instead of 120. There were obtained 128 grams of 94.8% cyanuric acid.

Example 5 Ether-alcohols of diethylene glycol other than the methyl ether are suitable for my process as is shown below.

180 g. of urea were added to 134 cc. of diethylene glycol monoethyl ether and the mixture heated under reflux for one hour. A slight precipitate was formed on cooling. 120 g. of urea were added and the mixture again heated under reflux for two hours. Cyanuric acid precipitated from the solution during this time. The slurry was cooled, 150 cc. of methanol were added, the slurry filtered and the cake washed with methanol and dried. The dry cyanuric acid weight was 85 g. The methanol was distilled off from the mother liquor and wash liquors, 120 g. of urea added to the residue remaining and the mixture heated to reflux for three hours. Cyanuric acid again precipitated. The slurry was cooled. 100 cc. of methanol was added and the slurry filtered. The cyanuric acid cake was washed with methanol and dried. The dry weight of the cake was 82 g.

Example 6 In the following example, there is first formed the in- 3 lterin'ediate' in a separate step although this is not necessary.

A mixture of 134 grams of diethylene glycol monoethyl ether and 60 grams of urea was heated under reflux. A homogeneous solution was obtained at 108 C. The temperature was raised from 140 C. to 220 C. in 65 minutes. No precipitation occurred. After cooling a further 120 grams of urea were added and the heating under reflux resumed. The temperature was raised from 140 C. to 235 C. in 79 minutes during which time cyanuric acid precipitated. The mixture was cooled, 100 cc. of methanol were added and the cyanuric acid filtered oil, washed with methanol and dried. Eighteen grams of cyanuric acid (80.5%) were obtained.

After distilling ed the methanol from the above mother liquor a further 120 grams of urea were added, the mixture heated under reflux and the temperature raised from 155 C. to 237 C. in 65 minutes. Cy-

treated by the same procedure used above. Seventyfour grams of cyanuric acid analyzing 97.0% were obtained.

Example 7 A mixture of 163 grams of diethylene glycol monoibutyl ether (1 mol.) and 190 grams of urea (3.166

from 127 C. to 237 C. in 65 minutes and precipitation occurred. To the cooled mixture 100 cc. of methanol were added, the solids filtered off, washed with methanol and dried. There were recovered 132 grams of cyanuric. acid analyzing 92.6%.

The methanol was distilled from the above mother liquor, 190 grams of urea were added and the mixture heated under reflux. A clear homogeneous solution was obtained at 129 C. The temperature was raised from 129 C. to 240 C. in 65 minutes with precipitation. After cooling, methanol was added, the solid filtered off, washed and dried. The weight of cyanuric acid obtained was 134 grams, its purity 92.5%.

The methanol was distilled from the above mother liquor and 130 grams of urea were added and the mixture heated under reflux as before. The temperature was raised from 212 C. to 244 C. in 44 minutes. Methanol was added to the cooled mixture and cyanuric acid recovered in the usual manner. The weight was 91 grams, the purity 96.3%.

Example 8 That better results are obtained at higher temperatures is confirmed by the series of runs described in the following example: I

A series of experiments similar to those of Example 7 was run with the following results:

Grade of Cyanurie Acid Time, Highest Temperature, 0. Min.

5 Example9 p U, Gram molecular weights of monobutyl ether of ethylene glycol (118 g.) and urea (60 g.) were heated together underreflux. At 169 the mixture became homogeneous. Heating was continued for 37 minutes more with the temperature rising to 193. Ammonia evolu tion had practically ceased and no precipitate occurred. 120 g. of urea were then added and heating resumed. At 126 C. the mixture was homogeneous. The term perature was raised to 215 C. in 73 minutes. Precipitation occurred. Ammonia evolution had practically ceased. After cooling, the precipitated cyanuric acid was recovered by the usual method. Eighty-three grams of 96.9% cyanuric acid were obtained. The mother liquor was available for further heating with additional urea.

Example 10 A mixture of 164 cc. of ethylene glycol mono hexyl ether and 60 grams of urea was heated under reflux from 121 C. to 191 C. in 38 minutes when the bottom layer had largely disappeared. A further 60 grams of urea were added and the mixture heated under reflux. The temperature was raised from 155 C. to 214 C. in 69 minutes. The mixture was allowed to cool and cc. of methanol were added. The mixture was filtered and the cyanuric acid cake washed with 100 cc. of methanol and dried. Fifty-four grams of cyanuric acid, 84% pure, were obtained.

Example 11 One hundred twentyeseven and a half grams of diethylene glycol (B.P. 242247 C.) and 144 grams of urea were heated under reflux. A clear homogeneous solution was obtained at C. The temperature was raised from 153 C. to 220 C. in 127 minutes. On cooling, 100 cc. of methanol were added and the mixture filtered. The cake was washed with'100 cc. of methanol and dried. Sixty-one grams of material was obtained.

The methanol was evaporated from the mother liquor, 100 grams of urea were added and the mixture heated under reflux. A clear homogeneous solution was obtained. at 140 C. The temperature was raised from 140 C. to 236 C. in 41 minutes. Solids precipitated. After cool ing, methanol was added, the solids filtered oil, washed with methanol and dried. There were obtained 59 grams of 96.9% cyanuric acid.

Example .12

A mixture of 100 grams of triethylene glycol and 160 grams of urea were heated under reflux. All the urea was in solution at C. The mixture was heated from 150 C. to 240 C. in 40 minutes. Precipitation took, place. It was cooled to 90 and 100 cc. of methanol added, filtered, the cake was washed with 100 cc. of methanol and dried. There were obtained 64 grams of cyanuric acid analyzing 92.2%.

The methanol was distilled from the above mother liquor, grams of urea added and heated under reflux.' The temperature rose from 160 C. to 233 C. in 49 ruinutes. Solids appeared. The mixture was cooled, v100 cc. of methanol were added. The solids were filtered oi. the cake washed with methanol and dried. There were obtained 85.5 grams of cyanuric acid analyzing 87.8%.

Example 13 A mixture of 178 grams of triethylene glycol ethyl ether and 60 grams of urea were heated under reflux;

reflux. The temperature was raised from C.to 245- C. in 61 minutes, during which time cyanuric acid precipitated. After cooling 100 cc. of methanol wereaddcd; the mixture was filtered, the cyanuric acid cake walla...

with methanol and dried. Fifty-six grams of 99% cyanuric acid were obtained.

The methanol was distilled from the above filtrate, 120 grams of urea were added and the mixture heated under reflux. The temperature was raised from 150- 245 in 35 minutes, during which interval cyanuric acid precipitated. The mixture was cooled, 100 cc. of methanol were added and the mixture filtered, the cake Washed with methanol and dried. Eighty-four grams of 94.1% cyanuric acid were obtained.

Example 14 The high molecular weight polyethylene glycols are also effective media. They are hydroxyethyl ethers of polyethylene glycols.

A mixture of 150 grams of polyethylene glycol and 60 grams of urea were heated under reflux. The polyethylene glycol used had an average molecular weight of 300 and was composed of a mixture of polyglycols of molecular weights fairly close to this average. A homogeneous solution was obtained at 120 C. The temperature was raised to 230 C. in 36 minutes. No precipitate formed. One hundred twenty grams additional of urea were added and the mixture heated under reflux. The temperature was raised from 155 C. to 250 C. in 48 minutes, during which time cyanuric acid was precipitated. The mixture was cooled, 100 cc. of methanol were added, the cyanuric acid filtered off, washed with methanol and dried. Ninety-two grams of cyanuric acid (96.9%) were obtained.

Example 15 A mixture of 175 grams of methoxypolyethylene glycol with a molecular weight range of 335-365 and 130 grams of urea was heated under reflux. A clear homogeneous solution was obtained at 130 C. The temperature was raised to 224 C. in thirteen minutes at which point cyanuric acid began to precipitate. The temperature was raised from 224 C. to 250 C. in minutes, at which time the ammonia evolution had practically ceased. The mixture was cooled, 200 cc. of methanol were added. The cyanuric acid was filtered, washed with methanol and dried. There were obtained 72 grams of 96.8% cyanuric acid.

The methanol was distilled from the above mother liquor and 130 grams of urea were added and the mixture heated under reflux. A clear homogeneous solution was obtained at 115 C. In twenty-three minutes the temperature reached 229 C. and cyanuric acid began to precipitate. The temperature of the mixture was raised from 229 C. to 260 C. in twenty-eight minutes, at which time the ammonia evolution had practically ceased. The mixture was allowed to cool, 100 cc. of methanol were added and the solids filtered off. The cyanuric acid cake was washed with methanol and dried. There were obtained 87 grams of 96.9% cyanuric acid.

There are certain individual characteristics of the various ether-alcohols that must be considered. If it is required to use any particular member of this series of compounds, the processing method must be adjusted to those characteristics. For example, the boiling point at atmospheric pressure of the methyl ether of ethylene glycol is so low that the carbamate forms from urea very slowly at this pressure so that superatmospheric pressure is preferably employed. Ether alcohols boiling over 140 can be easily used at atmospheric pressure. But it is preferred to use an ether-alcohol that can be used at atmospheric pressure and avoid the complications of pressure operation.

The maximum temperature of the reaction should be below the decomposition temperature of the ether-alcohol used, so that said temperature will vary depending on the ether-alcohol used.

Indirect methods of forming the carbamate media may be, used. For example, they may be formed by leading cyanuric acid vapors intothe ether-alcohol. Preferably,

the carbamate is formed by reacting the alcohol-ether with urea since this procedure involves no new reagents and can be conducted in the same vessel with the same equipment as the main reaction.

It is to be understood that by the term carbamate, the reaction product or products of ether-alcohol with urea is meant.

In the examples of this specification methanol is used to assist in the separation of cyanuric acid from the media. Various other volatile solvents for the carbamates may be used. Water may be used. In the removal of the water, care must be taken not to decompose the carbamate being recovered.

The process lends itself readily to continuous operation. This type of operation is preferred as it enables the maintenance of the desired temperatures during the addition of urea to the medium. On a commercial scale small amounts of the medium is withdrawn for purification in order to prevent the accumulation of too great a quan- Y tity of by-products. From this side stream the original alcohol-ethers can be recovered and returned to the process.

This application is a continuation-in-part of copending application, now abandoned, Serial No. 612,061, filed September 25, 1956, entitled Manufacture of Cyanuricf Acid.

What is claimed is: 1. A method of making cyanuric acid which comprises introducing urea into a solvent which is the reaction product of at least 1 mol. of urea with an ether alcohol having the formula:

wherein m=l to 6; n=1 to 17, ammonia being evolved; said solvent having a boiling point of at least C. under the pressure of the system, heating to not over 350 C., whereby cyanuric acid is precipitated and ammonia is evolved.

2. A method according to claim 1 in which monoalcohol having 1 to 3 carbon atoms is added to dissolve said solvent, and then separating said cyanuric acid from said medium.

3. A method according to claim 1 in which the temperature is maintained at about l50-300 C.

4. A method of making cyanuric acid which comprises introducing urea into a solvent which is the reaction product of at least 1 mol. of urea with an ether-alcohol having the formula;

wherein m=1 to 6; n=2 to 8, ammonia being evolved; said solvent having a boiling point of at least 160 C. under the pressure of the system, heating to not over 350 C., whereby cyanuric acid is precipitated and ammonia is evolved.

5. A method of making cyanuric acid which comprises introducing urea into a solvent which is the reaction product of at least 1 mol. of urea with an ether alcohol having the formula;

wherein m=1 to 6; n=1 to 8; and m-l-n is more than 3 when n=1, ammonia being evolved; said solvent having a boiling point of at least 160 C. under the pressure of the system, heating to not over 350 C., whereby cyanuric acid is precipitated and ammonia is evolved.

6. A method of making cyanuric acid which comprises introducing urea into a solvent which is the reaction product of at least 1 mol. of urea with an ether-alcohol having the formula:

wherein m=1 to 4; 12:1 to 8; and m+n is more than 3 when n=l, ammonia being evolved; said solvent having a boiling point of at least 160 C. under the pressure of the system, heating to not over 350 C. whereby cyanuric acid is precipitated and ammonia is envolved.

7. A method according to claim 1 in which the cyanuric acid is separated from the mother liquor, urea is added to said separated liquor, and the mass heated at temperatures of about 150-350 C. to cause evolution of ammonia and precipitation of cyanuric acid.

8. A method according to claim 1 in which the etheralcohol is taken from the class consisting of methyl, ethyl, butyl and hexyl ethers of ethylene glycol, diethylene glycol and triethylene glycol.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,479 Meigs Apr. 16, 1940 2,409,712 Schweitzer Oct. 22, 1946 2,802,022 Groszos et a1. Aug. 6, 1957 2,952,679 Perret Sept. 13, 1960 10 FOREIGN PATENTS 753,127 Germany Nov. 24, 1952 865,306 Germany Feb. 2, 1953 531,030 Great Britain Dec. 27, 1940 OTHER REFERENCES Hofmann: Dent. Chem. Gesel]. Berichte, vol. 4 (1871), page 267.

Grandiere: Bull. Soc. Chim. France, vol. 35, pp. 187- 196 (1924).

Conant: The Chemistry of Organic Compounds, revised edition 1939 (6th printing, 1943), The Macmillan 00., pages 252 to 254.

Metayer: Bull. Soc. Chim. France (Series 5), vol. 18, pages 802-806 (1951). 

1. A METHOD OF MAKING CYANURIC ACID WHICH COMPRISES INTRODUCING UREA INTO A SOLVENT WHICH IS THE REACTION PRODUCT OF AT LEAST 1 MOL. OF UREA WITH AN ETHER-ALCOHOL HAVING THE FORMULA: 